Field of the Invention
The present invention relates to a technique of mixing signals read out from a plurality of pixels from an image sensor used in an image capturing apparatus, such as a camera, and outputting a mixed signal.
Description of the Related Art
Conventionally, an image capturing apparatus capable of shooting an image at high frame rate by mixing pixel signals and reading out the mixed signals at high speed from an image sensor has been realized. Further, various counter measures to cope with problems that arises when mixing pixel signals have been proposed.
For example, Japanese Patent Laid-Open No. 2010-259027 proposes that, in a case where signals from a plurality of pixels arranged in the same column are simultaneously read out to a vertical output line to mix the pixel signals, a current value on the vertical output line is controlled to an optimum value in accordance with the number of pixels to be mixed. More specifically, the current on the vertical output line is increased in a case where the pixel signals are mixed comparing to a case where the pixel signals are not mixed. Further, as the number of pixels to be mixed is increased, the current on the vertical output line is increased, thereby expanding the optimum range for mixing pixel signals. The reason for changing the current in this manner is that, in a case where an amplitude of a pixel signal, in other words, of a signal on the vertical output line is large and a difference between pixel signals to be mixed is large, circuit current of the pixel producing a larger signal decreases, which prevents the pixel signals from being mixed correctly, and thus it is necessary to compensate for the shortage of current in the vertical output line.
However, in order to optimally mix pixel signals as disclosed in Japanese Patent Laid-Open No. 2010-259027, energy consumption greatly increases.